1. Technical Field
Systems and methods consistent with the present invention relate to a home-network and a method for assigning channels thereof, and more particularly, to a home-network that can offer improved image quality and performance of each device by adaptively allocating channels to each device depending on the sizes of frames in receiving, and a method for allocating channels thereof.
2. Related Art
In a related art home-network system, a home-network receives data from an external server. Among the data, multimedia data such as a moving picture is compressed into a frame unit, and the compressed data of frame unit is packetized into an Internet Protocol (IP) unit according to its capacity so as to be transmitted via IP network. Each compressed frame has different capacity according to a compression method, degree of movement of image, degree of association with the previous frames, and audio insertion. Accordingly, each frame may consist of a small or large number of packets according to its compressed size.
The related art process of transmitting the packetized data from the outer server to a certain device of the home-network will be explained with reference to FIG. 1.
In a related art home-network system, moving image data, audio data, and web data from the first moving image server, the second moving image server, Voice over Internet Protocol (VoIP) server, and Web server are transmitted via a router to a selected home-network from each of the servers, and the home gateway of the home-network transmits the data to each selected device.
The first moving image server tries to transmit the moving image data with a first frame of three packets a, a second frame of two packets b, and a third frame of one packet c to device 1 of the home-network. The second moving image server tries to transmit to device 2 the moving image data with a fourth frame of two packets d, a fifth frame of three packets e, and a sixth frame of one packet f. The VoIP server for transmitting audio data tries to transmit audio data F1, F2, F3 to device 3, and the web server tries to transmit web data to device 4.
As moving image data, audio data, and web data are delivered to the router from each server, the router outputs each data in real-time in the order of receiving, to transmit to the home gateway. For example, the router first transmits two packets a of the first frame of the first moving image server, transmits one data unit each of the web server and audio data F1, and then transmits the remaining one packet a of the first frame of the first moving image server. If the router transmits data from each server in real-time, a plurality of packets for one frame of the moving image data may be not sequentially transmitted.
If each data is delivered from the router via the IP network to the home gateway, the home gateway transmits the data via wireless network to each device in the home-network. At this time, the home gateway allocates channels in the order of receiving the data to transmit each data. Accordingly, the home gateway allocates two channels to transmit two packets a of the first frame from the first moving image server to the device 1, and then allocates one channel to transmit one packet d of the fourth frame from the second moving image server to the device 2. Then, the home gateway allocates one channel to transmit audio data F1 from the VoIP server to the device 3, and allocates one remaining packet a of the first frame from the first moving image server to the device 1.
According to the related art real-time data transmission method, two of the three packets of the first frame are firstly transmitted to the device 1, and then the remaining one packet is transmitted after the period of time during which three channels are allocated. Three packets for the first frame do not consecutively arrive at the device 1 but arrive separately, which can cause a delay in the delivery time. If a delay occurs, the probability of data loss may increase, and the data may need to be re-transmitted due to the data loss. Accordingly, the amount of data that must be stored in a buffer may increase. Therefore, it may be impossible to reproduce images when desired, or the image quality may suffer due to the delay of the moving image data.
To solve the above related art problems, packet prioritization has been used, in which transmitted data is prioritized.
According to the related art method of packet prioritization, each device of the home-network is prioritized, depending on the capacity of the transmitted data. For example, the device 1 is set to the first priority with data capacity of several megabytes, and the device 2 is set to the second priority which assures having a smaller data capacity than that of the device 1. The device 3 receives audio data from the VoIP server and is set to the highest priority to receive the audio data in real-time.
When priority is set, if moving image data, audio data, and web data are transmitted from each outer server as shown in FIG. 2, a router sequentially arranges each data in the order the data was received and transmits to the home gateway as the related art. The home gateway allocates channels according to the priority of a device to transmit data to each device. First, if the home gateway allocates the number of channels corresponding to the preset data capacity, for example, three channels to the device 1 with the first priority, three packets of the first frame from the first moving image server are transmitted to the device 1.
When the home gateway can allocate the number of channels corresponding to the preset data capacity, for example, two channels for the moving image data from the second moving image server with the second priority, two packets of the fourth frame from the second moving image server are transmitted to the device 2. If the audio data F1, F2 are transmitted from the VoIP server with the highest priority, the home gateway instantly allocates two channels to transmit the audio data to the device 3. If there is no data with higher priority and some channels are available for use, the home gateway allocates the remaining channels for the web data from the web server and transmit them to the device 4.
Likewise, if the data of the second frame and the third frame are received from the first moving image server, the home gateway allocates three channels as preset to transmit at once two packets of the second frame and one packet of the third frame. Then, if data of the fifth frame is received from the second moving image server with the second priority, the home gateway allocates two preset channels to firstly transmit two of three packets of the fifth frame. The home gateway delivers one remaining packet of the fifth frame from the second moving image server only after it first delivers real-time audio data F3, F4 from the VoIP server with the highest priority, web data received from the web server prior to the last packet of the fifth frame, and moving data from the first moving image server.
As described above, according to the related art packet prioritization, data is transmitted to each device depending on preset priority and data capacity. Accordingly, since three channels can be allocated to the device 1, two packets of the second frame and one packet of the third frame are sequentially transmitted to the device 1 despite the fact that they do not need be transmitted together. On the other hand, since only two channels can be allocated to the device 2, three packets of the fifth frame are transmitted separately as two packets and one packet despite the fact that they need to be delivered together. In other words, when the packet prioritization is applied, an excessive number of channels are allocated to the device with high priority, in spite of the limited number of channels available in a wireless network. This may lead to an unnecessary waste of channels, and a buffer overflow due to excess of buffer capacity allocated to each device.
As the result, the transmission rate of a server may slow down, which can consequently cause unnecessary control signals to be continuously generated. The performance of the device with sub-priority significantly deteriorates due to the small capacity of the data that can be transmitted at once. Even the data transmitted to the device with high priority is not guaranteed to be delivered as a whole frame unit. Therefore, it is very likely that when sequentially transmitting a plurality of frames, a portion of packet of the frame positioned at rear side may not be transmitted together. As the result, delay may occur.
Accordingly, when allocating channels in the home-network system, it is necessary to adaptively allocate channels according to the frame size of data transmitted to the home-network from each outer server, instead of presetting the data capacity and the priority of a device to prevent allocating too many channels to a device with high priority, and decreasing the performance of a device with sub-priority.